One conventional and well-known type of electrode holder employs an electrode spindle or shaft axially slidably supported within a hollow body, with the electrode shaft being urged outwardly by a compression spring which is disposed within and coacts between the body and the shaft. To effect transmission of welding current from the body to the shaft, a split conical collar is interposed between one end of the spring and an enlarged head on the shaft, which head and collar have opposed conical surfaces whereby the urging of the spring causes the split collar to be slidably urged radially outwardly for slidable engagement with the surrounding annular wall of the body. Current transmission is effected from the hollow body through the annular wall to the split collar, and thence through the contacting conical surfaces to the head of the shaft. This arrangement is illustrated by U.S. Pat. No. 3,632,958.
As a further variation of the electrode holder of the above type, there is often provided a second split conical collar interposed between the other end of the spring and the adjacent end of the tubular housing, with this second collar and housing end having conical walls, whereby this second collar is spring-urged radially inwardly due to the conical relationship for snug slidable engagement with the electrode shaft. Welding current is transmitted from the tubular housing through the contacting conical surfaces to the collar, and thence radially inwardly to the shaft. This arrangement is illustrated by FIG. 2 of U.S. Pat. No. 4,417,122.
With electrode holders of the type employing split conical collars functioning as the electrical contact members, it has been observed that maintaining proper electrical contact between the relatively slidable contact surfaces, specifically between the slidable conical contact surfaces, is difficult. For example, when using a split conical contact collar, the radial displacement of the collar segments necessarily changes the proper bearing engagement between the opposed conical surfaces since the conical surface on the split collar can obviously be perfectly theoretically generated only for one precise radius, and any deviation from this radius results in less than the theoretically optimum fit between the opposed conical surfaces. During actual utilization of electrode holders employing such conical contact surfaces, it has been observed that these surfaces necessarily generate substantial electrical resistance due to less than optimum slidable fit therebetween, whereupon this poor electrical contact necessarily result in undesired and oftentimes excessive heat build-up and an arcing condition, which in turn can result in premature failure or shortened life of the electrode holder.
Another disadvantage associated with electrode holders of the aforementioned type is caused by the fact that the current contact members, and the contact pressure which exists across at least the conical contact faces, is created by the same spring which axially urges the electrode shaft outwardly of the housing. The contact pressure on the conical faces is thus dependent on and variable in accordance with the position of the electrode shaft, which position obviously determines the compression and hence the magnitude of the restoring force of the spring.
Accordingly, it is an object of this invention to provide an improved electrode holder which overcomes the abovementioned disadvantages. More specifically, this invention relates to an improved electrode holder which is believed to provide more optimum slidable contact both between the housing and contact structure, and between the contact structure and electrode shaft, so as to permit more efficient transfer of electrical current from the housing to the electrode shaft throughout the complete range of shaft movement, whereby excessive and undesired heating and arcing at or in the vicinity of the contact surfaces can be avoided, and hence the overall life of the electrode holder can be significantly increased.
Another object of the present invention is to provide an improved electrode holder, as aforesaid, in which the contact pressure at the contact surfaces between both the housing and the electrode shaft is uniform through the complete stroke or displacement of the electrode shaft, and independent of the spring force which urges the electrode shaft axially, so as to optimize the current transfer efficiency and hence the life of the electrode holder.
A further object of the invention is to provide an improved electrode holder, as aforesaid, which is economical to manufacture and assemble, which is simple and dependable in operation, and which is simple and inexpensive to repair if necessary.
Other objects and purposes of the invention will be apparent to persons familiar with structures of this general type upon reading the following specification and inspecting the accompanying drawings.